If you are bodybuilding or practicing high-intensity cardio you should already be increasing fast twitch fiber size. Unless you are doing reps of 30.

Is there any merit to increase overall size with this (bodybuilding applications), or is it primarily for old time athletes trying to make a comeback like my Pops?

Could you clarify this statement a bit? The reason that ready-set-go fitness seems to focus very much on the older crowd is probably due to the fact that fast twitch muscles atrophy as we age (if you don't use it you lose it). As we know, older people have a problem with lack of muscle and strength, so bodybuilding/strength training becomes very beneficial as we age.

Heavy, heavy weights with low reps is the only way to really hit the fast twitch fibers.

You body follows a recruitment pattern when it comes to using muscle cells and motor units. Your body will always try to use slow twitch first, but depends on the weight lifted. Meaning the heavier the weight, the more fast twitch that will be recruited and the quicker they will be recruited.

Heavy, heavy weights with low reps is the only way to really hit the fast twitch fibers.

You body follows a recruitment pattern when it comes to using muscle cells and motor units. Your body will always try to use slow twitch first, but depends on the weight lifted. Meaning the heavier the weight, the more fast twitch that will be recruited and the quicker they will be recruited.

So it's not a matter of low weight and explosive reps? I was under that assumption... but I'll take your word if you're pretty sure on this.

bodybuilding's goal is the development of fast twitch fibers. thats why people who work out get bigger muscles. These fast twitch fibers are the ones that grow larger in diameter through weight training.

If you are doing reps higher than 15, you'd be hitting slow twitch fibers primarily.

"Fast glycolytic fibers are the last to be recruited because they are found in the large motor units. These fibers are not usually recruited unless a muscle is generating a large amount of force, as occurs in high intensity exercises such as weight-lifting or sprinting." -Human Physiology, Germann and Stanfield 2001 published by Benjamin Cummings

Crunch, Slow twitch fibers are the high oxidative ones meaning they're the ones that are the endurance fibers.

I know what fast and slow twitch fibers are, I've got a masters in ex phys.

Bodybuilding is quite different from weight-lifting or sprinting. I was talking about fiber type displacement differences in bodybuilders as compared to a normal human being. Bodybuilding is not an "explosive" sport. I imagine that when you your book refers to "weight lifters", they are referring to olympic lifting.

I'm not saying they don't have a large number of fast twitch fibers or slow twitch. Just that I thought I remembered hearing that they had a larger number of slow-twitch. I will research that some more tomorrow.

Your body adapts to whatever type of training you give it. Remember your body is always looking to be efficient. Look at a sprinter, marathon runner, a swimmer, and a gymnast. There's your answer. Just think about what the difference is between these 4 athletes. They are living examples of how to train slow twitch as well as fast.

There should be a button next to the Reps and Report Post buttons with a clown face... "Call In the Clown". Bobo would then be summoned to give a succinct one-line answer that clarifies the whole issue and makes all others look like the fools that we are. He does seem to have a knack for doing that anyway, though, even without the button.

Crunch although it's true bodybuilding is different from say sprinting there's a lot we can learn from that athlete. Upper body in a sprinter is usually well built but pale in comparison to their quads, glutes, and hams. What we have to look at is the leg training and grueling way those muslces are worked day in and day out. We should be asking how can they work those muscle groups everyday and still recover to get that kind of growth. THe answer is the amount of fast twitch muslce fibers they've created in their lower body.

Originally Posted by CRUNCH

I know what fast and slow twitch fibers are, I've got a masters in ex phys.

Bodybuilding is quite different from weight-lifting or sprinting. I was talking about fiber type displacement differences in bodybuilders as compared to a normal human being. Bodybuilding is not an "explosive" sport. I imagine that when you your book refers to "weight lifters", they are referring to olympic lifting.

I'm not saying they don't have a large number of fast twitch fibers or slow twitch. Just that I thought I remembered hearing that they had a larger number of slow-twitch. I will research that some more tomorrow.

In world-class sprinters or pro athletes of any sport for that matter, I think a lot of it comes down to recovery ability. They are able to recover from all those long grueling workouts and continue to get bigger, faster, and stronger.

Plus the genetic component to what kinds of fibers they were born with. Those sprinters had waaaay more fast-twitch cells in those legs (and everywhere else) since they were born.

Add those genetics with years of brutal workouts, and the dedication and determinitation to be the best, and you've got a world class athlete.

In world-class sprinters or pro athletes of any sport for that matter, I think a lot of it comes down to recovery ability. They are able to recover from all those long grueling workouts and continue to get bigger, faster, and stronger.

Plus the genetic component to what kinds of fibers they were born with. Those sprinters had waaaay more fast-twitch cells in those legs (and everywhere else) since they were born.

Add those genetics with years of brutal workouts, and the dedication and determinitation to be the best, and you've got a world class athlete.

I hear ya and agree completely so I think the answer to the orginal question is years of brutal training will increase your type II's

Does this mean If I lift heavy weights slowly I will become more slow?

As correctly stated fibers are recruited in a set pattern, it is load and force that recruits the fast twitch muscle fibers, speed is not a factor in so much that lifting faster will recruit more fast twitch fibers, in fact the opposite is true as faster lifting speeds, increase momentum thereby actually reducing the loads on the muscle and therefore limiting the amount of actual muscle fibers called into play.

Also reps higher then 15 will increase endurance? Incorrect, it is not the reps per se, but the time under load. Sets with TUL in excessive of 120 seconds will do more to increase endurance, so one has to consider rep cadence when accounting for rep ranges.

Does this mean If I lift heavy weights slowly I will become more slow?

As correctly stated fibers are recruited in a set pattern, it is load and force that recruits the fast twitch muscle fibers, speed is not a factor in so much that lifting faster will recruit more fast twitch fibers, in fact the opposite is true as faster lifting speeds, increase momentum thereby actually reducing the loads on the muscle and therefore limiting the amount of actual muscle fibers called into play.

Also reps higher then 15 will increase endurance? Incorrect, it is not the reps per se, but the time under load. Sets with TUL in excessive of 120 seconds will do more to increase endurance, so one has to consider rep cadence when accounting for rep ranges.

How would you define plyometrics?? Are they done slowly to improve speed?? If you do them slow as you imply, they will make you faster?? Is that right. Dr Chu would beg to differ with you. Heavy weights and explosive movements was written as two different things.

ALR has a lot of insight on this subject. Too bad he's busy these days and doesn't post much anymore (hint-hint Viperspit & FitnFirm )

Here's a little excerpt from Building the Perfect Beast (the original one):

Originally Posted by ALR in Building the Perfect Beast

Earlier we discussed muscle fiber types. We know there are two fiber types,
Type-I and Type-ll with each consisting of sub-types. Basically Type I are endurance
fibers with a low growth (size) potential. They respond to low weight loads, and sets
that achieve positive failure above 15-20 reps. Type II fibers are strength orientated
fibers with a high growth potential. They respond best to higher weight loads and
sets that achieve positive failure below 1 5 reps.
Like I said, this is basic. Type II fibers are the primary focal point in
bodybuilding since the goal is maximum size. This means utilizing a weight that
achieves maximum fiber recruitment and achieves positive failure at 1 5 reps or below.
However, there are three Type II fiber sub-types; a, b, and c. Each responds to
different and somewhat specific rep/load protocols. (1) Type Ma are mostly effected
by sets of 11 -1 5. (2) Type Mb are mostly affected by sets of 6-10. (3) And Type lIc are
mostly affected by sets of 1-5 reps.
Remember, these rep ranges refer to sets taken to positive failure. This is why
most training systems call for sets that result in positive failure in the 9-1 2 rep range.
Unfortunately 8-1 2 reps would mostly focus upon Type IIb fibers with some carry over
effects upon Type Ma and Type IIc muscle fibers.